Small-Scale Horizontal Variations in Ionic Concentrations of Bulk Deposition from Hong Kong

The concentrations of major anions andcations in bulk deposition were found to varyspatially by factors of up to 65, for two samplings at17 sampling sites separated by 45 km or less in theTerritory of Hong Kong. Under predominantly maritimeairstreams, these variations resulted from localemissions, as well as from lower seasaltconcentrations at the more northerly sites. The weakacidity of the bulk deposition resulted fromneutralization of hydrometeors by basic particulatematter, leading to an unusual anticorrelation of theconcentrations of non-seasalt sulphate and hydrogenions. Greater anthropogenic activity at inland andindustrial sites was generally marked by highernitrate concentrations, with the ratio of nitrate ionconcentrations from the two samplings being stronglycorrelated with that of calcium ion. Chloride lossincreased with increasing concentrations ofnon-seasalt nitrate and sulphate. Most of the variancein the bulk deposition data for 8 major anions andcations could be explained by 2 factors: seasalt andanthropogenic, in common with the 1997 EnvironmentalProtection Department data for these species in totalsuspended particulate matter. Results for 14 solubletrace metal species in the bulk deposition at thesites are also reported.